Semiconductor lasers have gained influence in high power laser applications because of their higher efficiency, advantages in Size, Weight And Power (SWAP) and their lower cost over other forms of high power lasers. Many laser applications such as industrial cutting and welding, Laser Detection and Ranging (LADAR), medical engineering, aviation defense, optically pumping rare earth doped fiber lasers, optically pumping solid state crystals in Diode Pumped Solid State lasers (DPSS), fiber-optic communication, and fusion research, among others, require a high power and high frequency response. Due to their high power array outputs, edge-emitting semiconductor lasers are widely used in such applications. However, degradation of these edge-emitting lasers is common, primarily as a result of Catastrophic Optical Damage (COD) that occurs due to high optical power density at the exposed emission facet.
VCSELs, in comparison, are not subject to COD because the gain region is embedded in the epitaxial structure and is therefore not exposed to the outside environment. Also, the optical waveguide associated with the edge-emitter junction has a relatively small area, resulting in significantly higher power densities compared to VCSELs. The practical result is that VCSELs can have lower failure rates than typical edge-emitting lasers.
To date, VCSELs have been more commonly used in data and telecommunications applications, which require higher frequency modulation, but not as much power. VCSELs have offered advantages over edge-emitting LASERs in this type of application, including ease of manufacture, higher reliability, and better high frequency modulation characteristics. Arrays of VCSELs can also be manufactured much more cost efficiently than edge-emitting laser arrays. However, with existing VCSEL designs, as the area of the array grows the frequency response has been penalized by heating complexities arising from the multi-element designs, parasitic impedances, and the frequency response of the wire bonds or leads required by the high current. Thus, the modulation frequency of the array decreases.
VCSELs and methods for manufacturing them are known. See, for example, U.S. Pat. Nos. 5,359,618 and 5,164,949, which are incorporated herein by reference. Forming VCSELs into two-dimensional arrays for data displays is also known. See U.S. Pat. Nos. 5,325,386 and 5,073,041, which are incorporated herein by reference. Flip-chip multibeam VCSEL arrays for higher output power have been mentioned, in particular, in U.S. Pat. No. 5,812,571, which are incorporated herein by reference.
However, VCSEL arrays that provide both high frequency modulation and high power have not been adequately developed. Furthermore, arraying such devices together increases heat generation, adding to the negative effects on high frequency operation.
In addition, to obtain high brightness pulsed VCSEL devices for Time of Flight (TOF) laser radar (LIDAR) and pulsed sensor source applications, single (fundamental) mode VCSEL devices are typically designed. Single mode devices, however, sacrifice total output power due to the reduced aperture sizes needed to create such devices, and when such devices are driven with a high input current, the transition to multimode operation is not ideal as the beam of light tends to have a donut hole profile where it is brighter in the center area of the beam and around the circumference area of the beam, but darker between these two areas.